Any list of the world’s top ten most famous paintings will surely include da Vinci’s Mona Lisa. Part of the painting’s appeal is its mystery.

Those lucky enough to have an unobstructed view of the Mona Lisa at the Louvre often stare in awe， baffled by the smile that seems to flicker and fade. Gazing at a reproduction of the work produces the same effect. Now she’s smiling， now she’s not.

What’s the deal with Mona Lisa’s smile？

Harvard neuroscientist Margaret Livingstone is pretty sure she has solved the puzzle. Presuming nothing， Livingstone reasons that the famous portrait’s flickering smile is caused by the way we see.

Our eyes use two separate regions to see. One is the fovea， a central area used to see colors and pick out details such as fine print. The area around the fovea is better at detecting motion， shadows， and stark， black and white contrasts.

When we look at a person’s face， according to Livingstone， we usually focus centrally on the eyes. Gazing at Mona Lisa’s eyes， our less accurate peripheral vision notices the mouth， picking up shadows from the cheekbones.

The shadows play visual tricks， hinting at the curve of a smile. But when we look directly at the mouth， our central vision doesn’t see the shadows， and so the smile suddenly disappears. As our eyes scan different parts of the portrait， Mona’s smile seems to fade in and out.

Did da Vinci intend to create this flickering smile effect？Perhaps. In any case， he was genius enough to paint shadows subtle enough to astound viewers for half a millennium. Meanwhile， Mona Lisa will keep smiling. And not.

在任何世界名畫前十名的列表中，一定都會有達芬奇的《蒙娜麗莎》。其吸引力部分來自于“蒙娜麗莎”的神秘。

那些有幸可以在盧浮宮自由欣賞蒙娜麗莎的人們眼神中常常都充滿了敬畏，他們也對蒙娜麗莎那看似轉瞬即逝的微笑感到困惑。即使看它的復制品也會產(chǎn)生同樣的效果——她笑了，她沒有笑。

蒙娜麗莎的微笑是怎么回事呢？

哈佛大學的神經(jīng)科學家瑪格麗特·利文斯通相當確信自己已經(jīng)解開了這個疑惑。其實沒什么其它原因，利文斯通將蒙娜麗莎轉瞬即逝的微笑產(chǎn)生的原因歸為“我們看它的方式”。

人是根據(jù)眼睛內(nèi)部兩個不同區(qū)域來分辨東西的。一個是視網(wǎng)膜中央凹，它是用來觀看顏色并察覺細節(jié)的中間地帶。而這個地帶周圍的區(qū)域則更擅長察覺位移、影子、光亮及黑白對比。

照利文斯通所說，當我們在注視一個人的臉時，我們經(jīng)常都會集中注意力在眼睛上。在凝視蒙娜麗莎的眼睛時，我們并不是那么精準的外圍視力就注意在嘴巴上了，而嘴巴上則覆有臉頰骨的陰影。

就是這個陰影在視覺上給我們開了玩笑，它（在嘴上）隱藏了微笑的曲線。但當我們直視她嘴巴的時候，我們的中心視力并不能看到陰影，所以微笑就立刻消失了。隨著觀看畫像的不同部位，蒙娜麗莎的微笑也就時有時無。

是達芬奇有意營造這么一個“似笑非笑”的效果嗎？或許吧。總之，他的天賦驚人異常，使他將陰影處理得如此微妙細致，以至讓觀賞者們震驚了半個世紀。而蒙娜麗莎的微笑，也會一直這樣時有時無。